The overall goal of this program is to define the cause of SIDS. With the recent discovery of abnormal LSD binding in the medulla of SIDS infants, we have focused our efforts on the medullary serotonergic system, to define what specifically happens to serotonergic neurons to cause them to malfunction. The goal of Project 5 is to define the cellular properties of serotonergic neurons, as a means of providing a neurobiological explanation for the link between serotonin and SIDS. We have previously demonstrated that serotenergic neurons closely apposed to large arteries in the rat ventral medulla increase their firing rate in response to acidosis, and we have proposed that they are chemoreceptors that stimulete breathing, arousal and other CNS changes to restore pH homeostasis: We now plan to use a rat model to determine whether the cellular properties of serotonergic neurons can explain the three risk factors in the Triple Risk Model for SIDS. We wiil use a combination of multielectrode arrays and patch clamp recordings from serotonergic neurons in culture and in brain slices. We will: 1) Study how different subsets of serotonergic neuron respond to acidosis, hypoxia, temperature and glucose. 2) Examine how muscarinic receptor activation leads to enhancement of chemoreception. 3) Define the changes in chemosensitity of serotonergic neurons as they undergo development. 4) Determine the effects of acute and chronic (during pregnancy) nicotine exposure on the function of serotonergic neurons. 5) Compare the cellular properties of serotonergic neurons from rats with those of piglets and mice, and determine whether serotonergic neurons from these species, as well as human infants, are closely associated with large arteries of the ventral medulla. These experiments will provide information critical to a full understanding of the role of serotonergic neurons in brain function, and will lead to specific testable hypotheses about how their malfunction or maldevelopment could lead to death during sleep. URimately, the results of these experiments may provide important insights that could lead to diagnostic and therapeutic tests for those infants at highest risk of SIDS.